Phenotypic and molecular characterization of Streptococcus pneumoniae serotype 3 isolates from blood and respiratory samples in Canada: CANWARD 2007-21.

BACKGROUND: Lower respiratory infections and invasive disease caused by Streptococcus pneumoniae serotype 3 remain major clinical challenges around the world, despite widespread availability of updated vaccines. METHODS: As part of CANWARD, antimicrobial susceptibility testing and serotyping were performed on all S. pneumoniae isolates from 2007 to 2021. A subset of 226/264 (85.6%) serotype 3 isolates were selected for WGS to determine sequence type (ST)/clonal cluster (CC) and correspondence of antimicrobial resistance determinants (erm, mefAE, tetM, cat, folA, folP) with resistance phenotype. RESULTS: Of the 3,039 S. pneumoniae isolates obtained from 2007 to 2021, 8.7% (n = 264) were serotype 3, with 64.0% of respiratory origin and 36.0% from blood. Of 226 sequenced serotype 3 isolates, 184 (81.4%) were ST180 (GPSC12). The proportion of ST8561 (single locus variant of ST180) increased from 7.2% to 16.6% during the study period. An increasing proportion of serotype 3 isolates had phenotypic resistance (P = 0.0007) and genetic resistance determinants (P = 0.004), comparing 2017-21 to 2007-11, largely due to a recently expanded ST180 clade with cat, tetM and mef determinants. CONCLUSIONS: S. pneumoniae serotype 3 from GPSC12 continues to dominate throughout Canada, with an increase in the proportion of ST8561. The proportion of serotype 3 isolates that are phenotypically resistant and with genetic resistance determinants is increasing over time, reflecting a global increase in GPSC12 genotypes with known resistance determinants. Phylogenomic characterization of isolates collected over time and from around the world may facilitate improved treatment and enhanced prevention strategies, including new vaccines with activity against S. pneumoniae serotype 3.

Evaluation of Whole Genome Sequencing-Based Predictions of Antimicrobial Resistance to TB First Line Agents: A Lesson from 5 Years of Data.

Phenotypic susceptibility testing of the Mycobacterium tuberculosis complex (MTBC) isolate requires culture growth, which can delay rapid detection of resistant cases. Whole genome sequencing (WGS) and data analysis pipelines can assist in predicting resistance to antimicrobials used in the treatment of tuberculosis (TB). This study compared phenotypic susceptibility testing results and WGS-based predictions of antimicrobial resistance (AMR) to four first-line antimicrobials-isoniazid, rifampin, ethambutol, and pyrazinamide-for MTBC isolates tested between the years 2018-2022. For this 5-year retrospective analysis, the WGS sensitivity for predicting resistance for isoniazid, rifampin, ethambutol, and pyrazinamide using Mykrobe was 86.7%, 100.0%, 100.0%, and 47.8%, respectively, and the specificity was 99.4%, 99.5%, 98.7%, and 99.9%, respectively. The predictive values improved slightly using Mykrobe corrections applied using TB Profiler, i.e., the WGS sensitivity for isoniazid, rifampin, ethambutol, and pyrazinamide was 92.31%, 100%, 100%, and 57.78%, respectively, and the specificity was 99.63%. 99.45%, 98.93%, and 99.93%, respectively. The utilization of WGS-based testing addresses concerns regarding test turnaround time and enables analysis for MTBC member identification, antimicrobial resistance prediction, detection of mixed cultures, and strain genotyping, all through a single laboratory test. WGS enables rapid resistance detection compared to traditional phenotypic susceptibility testing methods using the WHO TB mutation catalog, providing an insight into lesser-known mutations, which should be added to prediction databases as high-confidence mutations are recognized. The WGS-based methods can support TB elimination efforts in Canada and globally by ensuring the early start of appropriate treatment, rapidly limiting the spread of TB outbreaks.

Streptococcus pneumoniae serotyping and antimicrobial susceptibility: assessment for vaccine efficacy in Canada after the introduction of PCV13.

BACKGROUND: Streptococcus pneumoniae continues to be an important bacterial pathogen associated with invasive (e.g. bacteraemia, meningitis) and non-invasive (e.g. community-acquired respiratory tract) infections worldwide. Surveillance studies conducted nationally and globally assist in determining trends over geographical areas and allow comparisons between countries. OBJECTIVES: To characterize invasive isolates of S. pneumoniae in terms of their serotype, antimicrobial resistance, genotype and virulence and to use the serotype data to determine the level of coverage by different generations of pneumococcal vaccines. METHODS: SAVE (Streptococcus pneumoniae Serotyping and Antimicrobial Susceptibility: Assessment for Vaccine Efficacy in Canada) is an ongoing, annual, national collaborative study between the Canadian Antimicrobial Resistance Alliance (CARE) and the National Microbiology Laboratory, focused on characterizing invasive isolates of S. pneumoniae obtained across Canada. Clinical isolates from normally sterile sites were forwarded by participating hospital public health laboratories to the Public Health Agency of Canada-National Microbiology Laboratory and CARE for centralized phenotypic and genotypic investigation. RESULTS: The four articles in this Supplement provide a comprehensive examination of the changing patterns of antimicrobial resistance and MDR, serotype distribution, genotypic relatedness and virulence of invasive S. pneumoniae obtained across Canada over a 10 year period (2011-2020). CONCLUSIONS: The data highlight the evolution of S. pneumoniae under pressure by vaccination and antimicrobial usage, as well as vaccine coverage, allowing both clinicians and researchers nationally and globally to view the current status of invasive pneumococcal infections in Canada.

Analysis of MDR in the predominant Streptococcus pneumoniae serotypes in Canada: the SAVE study, 2011-2020.

OBJECTIVES: To investigate the levels of MDR in the predominant serotypes of invasive Streptococcus pneumoniae isolated in Canada over a 10 year period. METHODS: All isolates were serotyped and had antimicrobial susceptibility testing performed, in accordance with CLSI guidelines (M07-11 Ed., 2018). Complete susceptibility profiles were available for 13 712 isolates. MDR was defined as resistance to three or more classes of antimicrobial agents (penicillin MIC ≥2 mg/L defined as resistant). Serotypes were determined by Quellung reaction. RESULTS: In total, 14 138 invasive isolates of S. pneumoniae were tested in the SAVE study (S. pneumoniae Serotyping and Antimicrobial Susceptibility: Assessment for Vaccine Efficacy in Canada), a collaboration between the Canadian Antimicrobial Resistance Alliance and Public Health Agency of Canada-National Microbiology Laboratory. The rate of MDR S. pneumoniae in SAVE was 6.6% (902/13 712). Annual rates of MDR S. pneumoniae decreased between 2011 and 2015 (8.5% to 5.7%) and increased between 2016 and 2020 (3.9% to 9.4%). Serotypes 19A and 15A were the most common serotypes demonstrating MDR (25.4% and 23.5% of the MDR isolates, respectively); however, the serotype diversity index increased from 0.7 in 2011 to 0.9 in 2020 with a statistically significant linear increasing trend (P < 0.001). In 2020, MDR isolates were frequently serotypes 4 and 12F in addition to serotypes 15A and 19A. In 2020, 27.3%, 45.5%, 50.5%, 65.7% and 68.7% of invasive MDR S. pneumoniae were serotypes included in the PCV10, PCV13, PCV15, PCV20 and PPSV23 vaccines, respectively. CONCLUSIONS: Although current vaccine coverage of MDR S. pneumoniae in Canada is high, the increasing diversity of serotypes observed among the MDR isolates highlights the ability of S. pneumoniae to rapidly evolve.

Antimicrobial susceptibility testing of invasive isolates of Streptococcus pneumoniae from Canadian patients: the SAVE study, 2011-2020.

OBJECTIVES: To assess the antimicrobial susceptibility of 14 138 invasive Streptococcus pneumoniae isolates collected in Canada from 2011 to 2020. METHODS: Antimicrobial susceptibility testing was performed using the CLSI M07 broth microdilution reference method. MICs were interpreted using 2022 CLSI M100 breakpoints. RESULTS: In 2020, 90.1% and 98.6% of invasive pneumococci were penicillin-susceptible when MICs were interpreted using CLSI meningitis or oral and non-meningitis breakpoints, respectively; 96.9% (meningitis breakpoint) and 99.5% (non-meningitis breakpoint) of isolates were ceftriaxone-susceptible, and 99.9% were levofloxacin-susceptible. Numerically small, non-temporal, but statistically significant differences (P < 0.05) in the annual percentage of isolates susceptible to four of the 13 agents tested was observed across the 10-year study: chloramphenicol (4.4% difference), trimethoprim-sulfamethoxazole (3.9%), penicillin (non-meningitis breakpoint, 2.7%) and ceftriaxone (meningitis breakpoint, 2.7%; non-meningitis breakpoint, 1.2%). During the same period, annual differences in percent susceptible values for penicillin (meningitis and oral breakpoints) and all other agents did not achieve statistical significance. The percentage of isolates with an MDR phenotype (resistance to ≥3 antimicrobial classes) in 2011 and 2020 (8.5% and 9.4%) was not significantly different (P = 0.109), although there was a significant interim decrease observed between 2011 and 2015 (P < 0.001) followed by a significant increase between 2016 and 2020 (P < 0.001). Statistically significant associations were observed between resistance rates to most antimicrobial agents included in the MDR analysis (penicillin, clarithromycin, clindamycin, doxycycline, trimethoprim/sulfamethoxazole and chloramphenicol) and patient age, specimen source, geographic location in Canada or concurrent resistance to penicillin or clarithromycin, but not biological sex of patients. Given the large isolate collection studied, statistical significance did not necessarily imply clinical or public health significance in some analyses. CONCLUSIONS: Invasive pneumococcal isolates collected in Canada from 2011 to 2020 generally exhibited consistent in vitro susceptibility to commonly tested antimicrobial agents.

Comparison of PCV10, PCV13, PCV15, PCV20 and PPSV23 vaccine coverage of invasive Streptococcus pneumoniae isolate serotypes in Canada: the SAVE study, 2011-20.

BACKGROUND: As pneumococci evolve under vaccine, antimicrobial and other selective pressures, it is important to track isolates covered by established (PCV10, PCV13 and PPSV23) and new (PCV15 and PCV20) vaccine formulations. OBJECTIVES: To compare invasive pneumococcal disease (IPD) isolates from serotypes covered by PCV10, PCV13, PCV15, PCV20 and PPSV23, collected in Canada from 2011 to 2020, by demographic category and antimicrobial resistance phenotype. METHODS: IPD isolates from the SAVE study were initially collected by members of the Canadian Public Health Laboratory Network (CPHLN) as part of a collaboration between the Canadian Antimicrobial Resistance Alliance (CARA) and the Public Health Agency of Canada (PHAC). Serotypes were determined by quellung reaction, and antimicrobial susceptibility testing was performed using the CLSI broth microdilution method. RESULTS: A total of 14 138 invasive isolates were collected from 2011 to 2020, with 30.7% of isolates covered by the PCV13 vaccine, 43.6% of isolates covered by the PCV15 vaccine (including 12.9% non-PCV13 serotypes 22F and 33F), and 62.6% of isolates covered by the PCV20 vaccine (including 19.0% non-PCV15 serotypes 8, 10A, 11A, 12F and 15B/C). Non-PCV20 serotypes 2, 9N, 17F and 20, but not 6A (present in PPSV23) represented 8.8% of all IPD isolates. Higher-valency vaccine formulations covered significantly more isolates by age, sex, region and resistance phenotype including MDR isolates. Coverage of XDR isolates did not significantly differ between vaccine formulations. CONCLUSIONS: When compared with PCV13 and PCV15, PCV20 covered significantly more IPD isolates stratified by patient age, region, sex, individual antimicrobial resistance phenotypes and MDR phenotype.

Genomic investigation of the most common Streptococcus pneumoniae serotypes causing invasive infections in Canada: the SAVE study, 2011-2020.

OBJECTIVES: To investigate the lineages and genomic antimicrobial resistance (AMR) determinants of the 10 most common pneumococcal serotypes identified in Canada during the five most recent years of the SAVE study, in the context of the 10-year post-PCV13 period in Canada. METHODS: The 10 most common invasive Streptococcus pneumoniae serotypes collected by the SAVE study from 2016 to 2020 were 3, 22F, 9N, 8, 4, 12F, 19A, 33F, 23A and 15A. A random sample comprising ∼5% of each of these serotypes collected during each year of the full SAVE study (2011-2020) were selected for whole-genome sequencing (WGS) using the Illumina NextSeq platform. Phylogenomic analysis was performed using the SNVPhyl pipeline. WGS data were used to identify virulence genes of interest, sequence types, global pneumococcal sequence clusters (GPSC) and AMR determinants. RESULTS: Of the 10 serotypes analysed in this study, six increased significantly in prevalence from 2011 to 2020: 3, 4, 8, 9N, 23A and 33F (P ≤ 0.0201). Serotypes 12F and 15A remained stable in prevalence over time, while serotype 19A decreased in prevalence (P < 0.0001). The investigated serotypes represented four of the most prevalent international lineages causing non-vaccine serotype pneumococcal disease in the PCV13 era: GPSC3 (serotypes 8/33F), GPSC19 (22F), GPSC5 (23A) and GPSC26 (12F). Of these lineages, GPSC5 isolates were found to consistently possess the most AMR determinants. Commonly collected vaccine serotypes 3 and 4 were associated with GPSC12 and GPSC27, respectively. However, a more recently collected lineage of serotype 4 (GPSC192) was highly clonal and possessed AMR determinants. CONCLUSIONS: Continued genomic surveillance of S. pneumoniae in Canada is essential to monitor for the appearance of new and evolving lineages, including antimicrobial-resistant GPSC5 and GPSC162.

Evaluation of the Hologic Aptima Combo 2 Assay for Detection of Neisseria gonorrhoeae from Joint Fluid Specimens.

Gonorrhea is a sexually transmitted bacterial infection caused by Neisseria gonorrhoeae. Nucleic acid amplification testing is the preferred method for routine diagnosis of gonorrhea from urogenital specimens, but culture is commonly used for diagnosis of disseminated infections, including gonococcal arthritis. The Hologic Aptima Combo 2 (AC2), a transcription-mediated amplification assay, is FDA and Health Canada licensed for detection of N. gonorrhoeae and Chlamydia trachomatis from urogenital, rectal, and pharyngeal specimens, but not joint fluid. In the current study, we compared the performance of microscopy, culture, and the AC2 for detection of N. gonorrhoeae from 170 joint fluid specimens. A total of five specimens were culture-positive, whereas 14 were AC2-positive. Gram-negative diplococci, characteristic of Neisseria, were observed in only two joint fluid specimens. Complementary testing confirmed the presence of N. gonorrhoeae in seven discordant (i.e., culture-negative/AC2-positive) specimens. These results indicate that the AC2 is more sensitive than culture for the diagnosis of gonococcal arthritis.

In vitro activity of fosfomycin against bacterial pathogens isolated from urine specimens in Canada from 2007 to 2020: CANWARD surveillance study.

BACKGROUND: Multiple susceptible breakpoints are published to interpret fosfomycin MICs: ≤64 mg/L for Escherichia coli and Enterococcus faecalis grown from urine (CLSI M100); ≤32 mg/L for Enterobacterales and staphylococci when parenteral fosfomycin is prescribed (EUCAST); and ≤8 mg/L for uncomplicated urinary tract infection with E. coli when oral fosfomycin is used (EUCAST). Clinical laboratories are frequently requested to test fosfomycin against antimicrobial-resistant urinary isolates not included in standard documents. METHODS: The in vitro activity of fosfomycin was determined using the CLSI agar dilution method for a 2007-20 collection of clinically significant Gram-negative (3656 Enterobacterales; 140 Pseudomonas aeruginosa) and Gram-positive (346 E. faecalis; 94 Staphylococcus aureus) urinary isolates from the CANWARD surveillance study. Comparator agents were tested using CLSI broth microdilution. RESULTS: Using the CLSI MIC breakpoint (≤64 mg/L), 99.2% of E. coli (n = 2871; MIC90, 4 mg/L), including 96.7% of ESBL-positive isolates, were fosfomycin susceptible. Similarly, 95.8% of E. coli, including 95.2% of ESBL-positive isolates, were fosfomycin susceptible at ≤8 mg/L (EUCAST oral susceptible MIC breakpoint). All other species of Enterobacterales (except Citrobacter freundii) and P. aeruginosa had higher fosfomycin MICs (MIC90s, 64 to >512 mg/L) than E. coli. Using published breakpoints, 88.4% of E. faecalis (MIC ≤64 mg/L) and 97.9% of S. aureus (MIC ≤32 mg/L) isolates were fosfomycin susceptible. CONCLUSIONS: Fosfomycin demonstrated in vitro activity against frequently encountered Gram-positive and Gram-negative urinary pathogens; however, the extrapolation of current CLSI and EUCAST MIC breakpoints to pathogens not specified by standard methods requires further study and is currently not recommended.

In vitro activity of sulopenem against 1880 bacterial pathogens isolated from Canadian patients with urinary tract infections (CANWARD, 2014-21).

INTRODUCTION: There are limited oral antimicrobial options for the treatment of urinary infections caused by ESBL-producing and MDR Enterobacterales. Sulopenem is an investigational thiopenem antimicrobial that is being developed as both an oral and IV formulation. The purpose of this study was to evaluate the in vitro activity of sulopenem versus bacterial pathogens recovered from the urine of patients admitted to or assessed at hospitals across Canada (CANWARD). MATERIALS AND METHODS: The in vitro activity of sulopenem and clinically relevant comparators was determined for 1880 Gram-negative and Gram-positive urinary isolates obtained as part of the CANWARD study (2014 to 2021) using the CLSI broth microdilution method. RESULTS: Sulopenem demonstrated excellent in vitro activity versus members of the Enterobacterales, with MIC90 values ranging from 0.06 to 0.5 mg/L for all species tested. Over 90% of ESBL-producing, AmpC-producing and MDR (not susceptible to ≥1 antimicrobial from ≥3 classes) Escherichia coli were inhibited by ≤0.25 mg/L of sulopenem. Sulopenem had an identical MIC90 to meropenem for ESBL-producing and MDR E. coli. The MIC90 of sulopenem and meropenem versus MSSA was 0.25 mg/L. Sulopenem was not active in vitro versus Pseudomonas aeruginosa (similar to ertapenem), and it demonstrated poor activity versus Enterococcus faecalis (similar to meropenem). CONCLUSIONS: Sulopenem demonstrated excellent in vitro activity versus bacterial pathogens recovered from the urine of Canadian patients. These data suggest that sulopenem may have a role in the treatment of urinary infections caused by antimicrobial-resistant Enterobacterales, but additional clinical studies are required.

PCV-15 and PPSV-23 coverage of invasive and respiratory tract Streptococcus pneumoniae, including MDR and XDR isolates: CANWARD 2007-20.

OBJECTIVES: To compare the proportion of invasive and respiratory tract isolates of Streptococcus pneumoniae, including MDR and XDR strains, that demonstrated PCV-15 and PPSV-23 serotypes in Canada from 2007 to 2020. METHODS: The CANWARD study collected 2984 S. pneumoniae isolates from 2007 to 2020 (1054 invasive, 1930 respiratory). Serotyping was performed using the Quellung reaction. Antimicrobial susceptibility testing was performed using CLSI methods. MDR/XDR was defined as resistance to ≥3/≥5 antimicrobial classes, respectively. RESULTS: Overall, the proportion of vaccine serotypes demonstrating a PCV-15/PPSV-23 serotype was significantly higher in blood isolates (54.6%/76.2%, respectively) than respiratory isolates (38.9%/55.3%; P < 0.0001). Similarly, PCV-15 and PPSV-23 vaccine coverage was higher for blood isolates for all demographic categories, including both genders, all regions and all age groups (P ≤ 0.0213). PCV-15/PPSV-23 coverage was also significantly higher for blood isolates demonstrating clarithromycin resistance (60.4/75.1% blood, 47.8/57.4% respiratory; P ≤ 0.009) and penicillin resistance (68.9/63.0% blood, 45.2/43.0% respiratory; P < 0.0001) and trimethoprim/sulfamethoxazole-resistant isolates for PPSV-23 only (82.6% blood, 64.3% respiratory; P = 0.0057). Vaccine coverage was numerically higher but not significantly different between specimen source for children <2 years of age, as well as ceftriaxone-, doxycycline- and levofloxacin-resistant isolates. PCV-15/PPSV-23 vaccine coverage for MDR isolates (61.8%/67.3% blood, 52.2%/56.2% respiratory) and XDR isolates (93.3% blood, 89.6% respiratory for both vaccines) was not significantly different between specimen sources. CONCLUSIONS: PCV-15 and PPSV-23 serotype coverage is generally greater for blood versus respiratory isolates but not for MDR and XDR isolates. Continued pneumococcal surveillance is warranted to determine future trends in vaccine coverage, serotype distribution and antimicrobial susceptibilities under the pressure of vaccine use.

Compilation of 10 Years of MIRU-VNTR Data: Canadian National Tuberculosis Laboratory's Experience.

Tuberculosis is a significant cause of morbidity worldwide and is a priority at the provincial and federal levels in Canada. It is known that tuberculosis transmission networks are complex and span many years as well as different jurisdictions and countries. MIRU-VNTR is a universal tuberculosis genotyping method that utilizes a 24-loci pattern and it has shown promise in identifying inter and intrajurisdictional clusters within Canada. MIRU-VNTR data collected over 10 years from the National Reference Centre for Mycobacteriology (NRCM) were analyzed in this study. Some clusters were unique to a single province/territory, while others spanned multiple provinces and/or territories in Canada. The use of a universal laboratory test can enhance contact tracing, provide geographical information on circulating genotypes, and hence, aid in tuberculosis investigation by public health. The housing of all data on one platform, technical ease of the method, easy exchange of data between jurisdictions, and strong collaboration with laboratories and surveillance units at the provincial and federal levels have the potential to identify possible outbreaks in real time.

Use of Fosfomycin Etest To Determine In Vitro Susceptibility of Clinical Isolates of Enterobacterales Other than Escherichia coli, Nonfermenting Gram-Negative Bacilli, and Gram-Positive Cocci.

Clinical isolates of Enterobacterales other than Escherichia coli (EOTEC), nonfermenting Gram-negative bacilli, and Gram-positive cocci were tested for susceptibility to fosfomycin using Etest and reference agar dilution. Applying EUCAST (v. 11.0, 2021) intravenous fosfomycin breakpoints, Etest MICs for EOTEC showed essential agreement (EA), categorical agreement (CA), major error (ME), and very major error (VME) rates of 70.4%, 88.4%, 4.1%, and 32.1%, respectively. No species of EOTEC tested with acceptable rates for all of EA (≥90%), CA (≥90%), ME (≤3%), and VME (≤3%). Etest MICs for Enterococcus faecalis, interpreted using CLSI oral/urine criteria (M100, 2021) showed EA, CA, minor error, ME, and VME rates of 98.5%, 81.2%, 18.8%, 0%, and 0%. Against Staphylococcus aureus, EA, CA, and ME rates were 84.1%, 98.7%, and 1.3% (EUCAST intravenous criteria). S. aureus isolates with fosfomycin MICs of >32 µg/ml (resistant) were not identified by agar dilution. We conclude that performing fosfomycin Etest on isolates of S. aureus will reliably identify fosfomycin-susceptible isolates with low, acceptable rates of MEs and VMEs. Testing of urinary isolates of E. faecalis by Etest is associated with an unacceptably high rate of minor errors (18.8%) but low, acceptable rates of MEs and VMEs when results are interpreted using CLSI criteria. Isolates of EOTEC tested by Etest with resulting MICs interpreted by EUCAST criteria were associated with an unacceptably high VME rate (32.1%). In vitro testing of clinical isolates beyond E. coli, E. faecalis, and S. aureus to determine susceptibility to fosfomycin is problematic with current methods and breakpoints.

In vitro activity and resistance rates of topical antimicrobials fusidic acid, mupirocin and ozenoxacin against skin and soft tissue infection pathogens obtained across Canada (CANWARD 2007-18).

BACKGROUND: Current antimicrobial susceptibility/resistance data versus skin and soft tissue infection (SSTI) pathogens help to guide empirical treatment using topical antimicrobials. OBJECTIVES: To assess the in vitro activity and resistance rates of fusidic acid, mupirocin, ozenoxacin and comparator agents against pathogens isolated from patients with SSTIs in Canada. METHODS: SSTI isolates of MSSA (n = 422), MRSA (n = 283) and Streptococcus pyogenes (n = 46) obtained from CANWARD 2007-18 were tested using CLSI broth microdilution. Fusidic acid low-level resistance was defined as an MIC of ≥2 mg/L and high-level resistance as an MIC ≥512 mg/L. Mupirocin high-level resistance was defined as an MIC ≥512 mg/L and low-level resistance was an MIC of 2-256 mg/L. RESULTS: Low-level and high-level fusidic acid resistance in MSSA was 10.9% and 1.7%, respectively. Low-level and high-level fusidic acid resistance in MRSA was 10.6% and 3.5%, respectively. High-level mupirocin resistance was identified in 1.4% of MSSA and 14.1% of MRSA, respectively. Versus MSSA, ozenoxacin demonstrated MIC50 and MIC90 of 0.004 and 0.25 mg/L, respectively. Against MRSA, ozenoxacin inhibited all isolates at an MIC of ≤0.5 mg/L, including isolates with ciprofloxacin MICs >2 mg/L, clarithromycin-resistant, clindamycin-resistant, high-level fusidic acid-resistant and high-level mupirocin-resistant isolates. CONCLUSIONS: We conclude that fusidic acid low-level resistance exceeded 10% for both MSSA and MRSA while fusidic acid high-level resistance was ≤3.5%. Mupirocin high-level resistance exceeded 10% in MRSA. Ozenoxacin is active versus SSTI pathogens including MRSA resistant to fluoroquinolones, macrolides, clindamycin, fusidic acid and mupirocin.

ESBL-positive Escherichia coli and Klebsiella pneumoniae isolates from across Canada: CANWARD surveillance study, 2007-18.

OBJECTIVES: ESBL-producing Escherichia coli and Klebsiella pneumoniae are pathogens of increasing importance in Canada and elsewhere in the world. The purpose of this study was to phenotypically and molecularly characterize ESBL-producing E. coli and K. pneumoniae clinical isolates obtained from patients attending Canadian hospitals over a 12 year period. METHODS: Isolates were collected between January 2007 and December 2018 as part of an ongoing national surveillance study (CANWARD). ESBL production was confirmed using the CLSI (M100) phenotypic method. Susceptibility testing was carried out using custom broth microdilution panels, and all isolates underwent WGS. RESULTS: In total, 671 E. coli and 141 K. pneumoniae were confirmed to be ESBL producers. The annual proportion of ESBL-producing isolates increased for both E. coli (from 3.3% in 2007 to 11.2% in 2018; P < 0.0001) and K. pneumoniae (from 1.3% in 2007 to 9.3% in 2018; P < 0.0001). The most frequent STs were ST131 for E. coli [62.4% (419/671) of isolates] and ST11 [7.8% (11/141)] and ST147 [7.8% (11/141)] for K. pneumoniae. Overall, 97.2% of ESBL-producing E. coli and K. pneumoniae isolates were MDR. blaCTX-M-15 predominated in both ESBL-producing E. coli (62.3% of isolates) and ESBL-producing K. pneumoniae (48.9% of isolates). CONCLUSIONS: The proportion of ESBL-producing E. coli, especially ST131, and K. pneumoniae, especially ST11 and ST147, in Canada increased significantly from 2007 to 2018. Continued prospective surveillance of these evolving MDR and at times XDR pathogens is imperative.

Comparison of phenotypic antimicrobial susceptibility testing results and WGS-derived genotypic resistance profiles for a cohort of ESBL-producing Escherichia coli collected from Canadian hospitals: CANWARD 2007-18.

OBJECTIVES: To determine whether the genotypic resistance profile inferred from WGS could accurately predict phenotypic resistance for ESBL-producing Escherichia coli isolated from patient samples in Canadian hospital laboratories. METHODS: As part of the ongoing CANWARD study, 671 E. coli were collected and phenotypically confirmed as ESBL producers using CLSI M100 disc testing criteria. Isolates were sequenced using the Illumina MiSeq platform, resulting in 636 high-quality genomes for comparison. Using a rules-based approach, the genotypic resistance profile was compared with the phenotypic resistance interpretation generated using the CLSI broth microdilution method for ceftriaxone, ciprofloxacin, gentamicin and trimethoprim/sulfamethoxazole. RESULTS: The most common genes associated with non-susceptibility to ceftriaxone, gentamicin and trimethoprim/sulfamethoxazole were CTX-M-15 (n = 391), aac(3)-IIa + aac(6')-Ib-cr (n = 121) and dfrA17 + sul1 (n = 169), respectively. Ciprofloxacin non-susceptibility was most commonly attributed to alterations in both gyrA (S83L + D87N) and parC (S80I + E84V), with (n = 187) or without (n = 197) aac(6')-Ib-cr. Categorical agreement (susceptible or non-susceptible) between actual and predicted phenotype was 95.6%, 98.9%, 97.6% and 88.8% for ceftriaxone, ciprofloxacin, gentamicin and trimethoprim/sulfamethoxazole, respectively. Only ciprofloxacin results (susceptible or non-susceptible) were predicted with major error (ME) and very major error (VME) rates of <3%: ciprofloxacin (ME, 1.5%; VME, 1.1%); gentamicin (ME, 0.8%-31.7%; VME, 4.8%); ceftriaxone (ME, 81.8%; VME, 3.0%); and trimethoprim/sulfamethoxazole (ME, 0.9%-23.0%; VME, 5.2%-8.5%). CONCLUSIONS: Our rules-based approach for predicting a resistance phenotype from WGS performed well for ciprofloxacin, with categorical agreement of 98.9%, an ME rate of 1.5% and a VME rate of 1.1%. Although high categorical agreements were also obtained for gentamicin, ceftriaxone and trimethoprim/sulfamethoxazole, ME and/or VME rates were ≥3%.

Susceptibility of Clinical Isolates of Escherichia coli to Fosfomycin as Measured by Four In Vitro Testing Methods.

Clinical isolates of Escherichia coli (n = 554) were tested against fosfomycin using agar dilution, disk diffusion, and Etest. Agar dilution (reference method) identified few isolates with fosfomycin MICs of 64 (n = 3), 128 (n = 4), and ≥256 µg/ml (n = 2). Applying CLSI (M100, 2020) and EUCAST (v. 10.0, 2020) breakpoints, 98.9% and 98.4% (agar dilution), 99.3% and 99.1% (disk diffusion), and 99.1% and 98.9% (Etest) of isolates were fosfomycin susceptible, respectively. Essential agreement (agar dilution versus Etest) was low (40.8%); 59.3% (131/221) of isolates with agar dilution MICs of 2 to 128 µg/ml tested 2 to 4 doubling dilutions lower by Etest. Applying CLSI breakpoints, categorical agreement was >99% for both disk diffusion and Etest; no major errors (MEs) or very major errors (VMEs) were identified, and rates of minor errors (mEs) were <1%. EUCAST breakpoints yielded categorical agreements of >99% and no MEs for both disk diffusion and Etest; however, VMEs occurred at unacceptable rates of 44.4% (disk diffusion) and 33.3% (Etest). All isolates with agar dilution MICs of ≥32 µg/ml (n = 12) and a subset of isolates with MICs of ≤16 µg/ml (n = 49) were also tested using the Vitek 2 AST-N391 card and generated fosfomycin MICs 1 to ≥3 doubling dilutions lower than agar dilution for 11/12 isolates with agar dilution MICs of ≥32 µg/ml. We conclude that performing fosfomycin disk diffusion or Etest on urinary isolates of E. coli and interpreting results using CLSI breakpoints reliably identified fosfomycin-susceptible isolates regardless of differences in endpoint reading criteria. EUCAST breakpoints generated excessive rates of VMEs for our isolate collection of high fosfomycin susceptibility.

Antimicrobial susceptibility of Clostridioides difficile isolated from diarrhoeal stool specimens of Canadian patients: summary of results from the Canadian Clostridioides difficile (CAN-DIFF) surveillance study from 2013 to 2017.

OBJECTIVES: To summarize data generated by the Canadian Clostridioides difficile (CAN-DIFF) surveillance study from 2013 to 2017. METHODS: Isolates of C. difficile (n = 2158) were cultured from toxin-positive diarrhoeal stool specimens submitted by eight hospital laboratories to a coordinating laboratory. Antimicrobial susceptibility testing was performed according to the CLSI agar dilution method (M11, 2018). Isolate ribotypes were determined using an international, standardized, high-resolution capillary gel-based electrophoresis protocol. RESULTS: Of the 2158 isolates of C. difficile, 2133 (98.8%) had vancomycin MICs ≤2 mg/L [i.e. were vancomycin susceptible (EUCAST breakpoint tables, v 9.0, 2019) or WT (CLSI M100, 29th edition, 2019)]. Fidaxomicin MICs were lower than those of all other agents tested (MIC90, 0.5 mg/L); however, one isolate with a fidaxomicin MIC of >8 mg/L was identified. Metronidazole MICs ranged from 0.12 to 4 mg/L; all isolates were metronidazole susceptible by the CLSI breakpoint (≤8 mg/L) compared with 96.8% susceptible by the EUCAST breakpoint (≤2 mg/L). In total, 182 different ribotypes were identified from 2013 to 2017. The most common ribotypes identified were 027 (19.3% of isolates) and 106 (8.2%). Ribotype 027 isolates were frequently moxifloxacin resistant (87.3% of isolates) and MDR (48.6%), associated with vancomycin (10/25, 40.0%) and metronidazole (58/69, 84.1%) resistance and from patients aged ≥80 years. The prevalence of ribotype 027 decreased significantly (P < 0.0001) from 2013 (27.5%) to 2017 (9.0%) and was replaced by increases in ribotype 106 (P = 0.0003) and multiple less common ribotypes. CONCLUSIONS: Periodic surveillance is required to monitor clinical isolates of C. difficile for changes to in vitro susceptibility testing profiles and ribotype evolution.

In Vitro Activity of Plazomicin against Gram-Negative and Gram-Positive Bacterial Pathogens Isolated from Patients in Canadian Hospitals from 2013 to 2017 as Part of the CANWARD Surveillance Study.

The Clinical and Laboratory Standards Institute (CLSI) broth microdilution method was used to evaluate the in vitro activities of plazomicin and comparator antimicrobial agents against 7,712 Gram-negative and 4,481 Gram-positive bacterial pathogens obtained from 2013 to 2017 from patients in Canadian hospitals as part of the CANWARD Surveillance Study. Plazomicin demonstrated potent in vitro activity against Enterobacteriaceae (MIC90 ≤ 1 µg/ml for all species tested except Proteus mirabilis and Morganella morganii), including aminoglycoside-nonsusceptible, extended-spectrum ß-lactamase (ESBL)-positive, and multidrug-resistant (MDR) isolates. Plazomicin was equally active against methicillin-susceptible and methicillin-resistant isolates of Staphylococcus aureus.

In Vitro Activity of Sulopenem, an Oral Penem, against Urinary Isolates of Escherichia coli.

The in vitro activity of sulopenem was assessed against a collection from 2014 to 2016 of 539 urinary isolates of Escherichia coli from Canadian patients by using CLSI-defined broth microdilution methodology. A concentration of sulopenem 0.03 µg/ml inhibited both 50% (MIC50) and 90% (MIC90) of isolates tested; sulopenem MICs ranged from 0.015 to 0.25 µg/ml. The in vitro activity of sulopenem was unaffected by nonsusceptibility to trimethoprim-sulfamethoxazole and/or ciprofloxacin, multidrug-resistant phenotypes, extended-spectrum ß-lactamases, or AmpC ß-lactamases.